If I take the physics GRE in October, decide to cancel the scores, and then take it again in November, will there be any record of me taking the test and cancelling my scores in October when I send my November results to schools?

IMO it's a great idea to register for bother the October and November tests and do what you're planning. I did this and it felt a little bit less stressful in October knowing I'd have another opportunity if it was a disaster... but I didn't need it. So I canceled the November test and got half the $ back.

A word on the revised general test: cancelled test scores will show up on future reports. There will be no scores associated with them, but it will indicate that you took the test and cancelled your score.